Power Integrated Circuit (PIC) refers to the Integrated Circuit which integrates high-voltage Power devices, signal processing system and peripheral interface circuit, protection circuit, detection and diagnosis circuit and other circuits in the same chip. It is divided generally into Smart Power Integrated Circuit (SPIC) and High Voltage Integrated Circuit (HVIC). Power integrated IC is widely used in power management, motor drive, automotive electronics, industrial control and other fields. BCD process refers to the process of integrating Bipolar, CMOS, DMOS and other high-voltage power devices, various resistance and capacitors, diodes into the same chip, which featured low cost, easy packaging and design, the simpler peripheral chips, rapidly developing into the mainstream technology in the power IC field, Bipolar transistors in BCD technology have high precision mainly used in analog circuits, CMOS have high integration mainly used in logic circuits, and DMOS have high power (high voltage) characteristics used commonly as a switch. DMOS used for switching is the core device of BCD technology. The function of DMOS requires that the device have high breakdown voltage and minimum specific conduction resistance. The performance of DMOS directly determines the driving capacity and area of the chip, so the design of DMOS is a key at the BCD technology. Because the BCD technology integrated the different function devices, so it requires the different working environment of a same chip, how to isolate different devices is another key in the design of BCD technology.